Rupture disc assembly

ABSTRACT

Disclosed is a rupture disc assembly for use in making a temporary seal in a vessel such as a casing string. The rupture disc assembly may generally include (A) a rupture disc having a side surface having a shallow taper inward towards a bottom surface of the rupture disc (B) an actuating mechanism including (i) an outer sled having an inner supporting surface forming a taper complimentary to the shallow taper of the side surface, (ii) an inner sled disposed within the outer sled and having a support shoulder to support the bottom surface of the rupture disc and (iii) a securing mechanism and (C) a housing to house the rupture disc and actuating mechanism.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 63/002,271 filed on Mar. 30, 2020, U.S. ProvisionalPatent Application Ser. No. 63/064,841 filed on Aug. 12, 2020 and U.S.Provisional Patent Application Ser. No. 63/155,266 filed on Mar. 1,2021. The contents of the aforementioned applications are incorporatedherein by reference.

FIELD

This disclosure relates to a rupture disc assembly for use in making atemporary seal in a vessel, for example in pipe such as tubing, casingand drill pipe, used in wellbore applications, for example in a casingstring, to temporarily seal a buoyant chamber beneath the rupture discassembly in the casing string.

BACKGROUND

A wellbore is a relatively deep and narrow hole that is typicallydrilled into the ground, often to locate and extract a resource, such aswater, gas, or oil, from a reservoir. A wellbore is often lined with alength of a pipe (often referred to as a casing) to help stabilize thewellbore and/or to prevent fluid loss to the surrounding earth.Nonetheless, it may be difficult to run a casing to great depths in awellbore because friction between the wellbore and the casing canprovide a substantial amount of drag. This is particularly true inhorizontal and/or deviated wellbores. In some situations, the drag onthe casing can exceed the available weight in a vertical segment of thewellbore. Also, segments in wellbores are not necessarily drilledstraight and may end up more helical during drilling, and this maycontribute to the drag on the casing as well. If there is insufficientweight in the vertical segment of the wellbore, it may be difficult orimpossible to overcome the drag in the horizontal leg of the wellboreand land the casing at a desired depth, such as for example, the toe ofa well. Failing to land the casing at the toe of the wellbore results ina loss of direct access to a formation surrounding the toe of the wellwhich can reduce production capacity of the reservoir.

One approach for mitigating casing drag is to lighten or “float” aportion of the casing in the wellbore, thereby creating a buoyantchamber within the casing, for example at a portion of the casing thatis meant to be driven around a heel of the wellbore to land in ahorizontal segment of the wellbore. The buoyant chamber can span some orall of the horizontal segment and may also include the heel and aportion of the vertical segment as well. A buoyant chamber can be formedwithin this portion of the casing by placing two spaced apart seals orplugs within a lower portion to seal in a low density fluid (for e.g.air) within the chamber. This buoyant chamber is run into the wellboreand is advanced toward the toe of the well as further joints of casingare added from surface. To drive the casing and buoyant chamber furtherinto the wellbore and past the heel into the horizontal segment of thewellbore, a higher density fluid may be pumped into the casing above thebuoyant chamber to add weight and drive the casing further toward thetoe of the wellbore. This method of floating the horizontal segment ofcasing reduces drag for the buoyant chamber/casing. After the casing haslanded, the buoyant chamber is no longer needed and can be removed,particularly for example, by removing a plug at the up-hole end of thecasing to allow the wellbore fluids to mix. The well is then cemented toisolate the annulus, by pumping cement into the wellbore, through thetoe of the well, and into the annular space between the wellbore and thecasing. A wiper plug is pumped downhole after the cement to drive cementremaining in the wellbore through the toe of the well, leaving thecasing inner diameter open, but with the casing annulus cemented forisolation purposes.

An existing technique for removing the plugged ends of the buoyantchamber is to drill them out. In some cases, a packer is used to sealthe casing above the buoyant chamber. The packer may be removed from thecasing string using a conventional drill-type work string, for example.Drilling out the plugged ends of the buoyant chamber adds an operationalstep to the completion process, increasing completion time cost, andrisk.

Another approach is to design a plugged end that can be destroyedwithout drilling. For example, a plugged end can be configured as arupture assembly capable of withstanding nominal hydrostatic pressure ofthe column of fluid above, while the pipe (for e.g. casing) is beingmoved into the wellbore, but that is also capable of breaking whensubjected to a higher force/pressure, such as a threshold hydraulicpressure that is intentionally produced in the column of fluid above therupture assembly using a hydraulic pump for example. In order to sustainhigh pressures while the pipe (e.g. casing) is being moved into thewellbore, the rupture disc assembly can be designed to be relativelythick or otherwise resistant to breakage under operational conditionsduring run-in of casing.

As completion technology improves, operators may wish to drilldeeper/longer wells and produce from longer horizontal segments under avariety of pressure and temperature conditions without introducing newsteps, costs, or operational risks. Therefore, it is desired tocontinuously improve the performance and reliability of rupture systemsused in casing buoyancy applications. Rupture systems that can beadapted to a variety of well applications, and/or that limit the volumeand/or particle size of debris released to the wellbore, and/or increasethe pressure competency of the rupture assembly would be desirable. Highpressure competency of the rupture assembly will allow the buoyantchamber to withstand relatively high hydraulic pressures during thepositioning of the casing in the wellbore and may also have aburst/breakage pressure which is significantly higher than the pressurerequired to activate the mechanism which causes the rupture discassembly to commence its failure mode/mechanism.

Rupture disc devices are also used in various other applications,including running them on drill pipe during an installation of a linerhanger or in other oilfield/gas field applications.

SUMMARY

The present disclosure is generally directed to a rupture disc assemblyfor use in forming a temporary seal in a vessel. The rupture discassembly is operable to change from a sealing mode in which thetemporary seal is formed to a release mode in which one or morecomponents of the rupture disc assembly are released from their positionin the sealing mode and to a disc failure mode in which the temporaryseal is broken.

The rupture disc assembly generally includes a rupture disc having apressure facing surface, a bottom surface, and a side surface having ashallow taper inward towards the bottom surface of the rupture disc.

The rupture disc assembly also includes an actuating mechanismconfigured to support the rupture disc and operable to be activated tochange the rupture disc assembly from the sealing mode to the releasemode and to the disc failure mode when the pressure facing surface ofthe rupture disc is subjected to a disc failure trigger pressure. Theactuating mechanism includes: (i) an outer sled operable to move in adownhole direction from a first position to a second position afteractivation of the actuating mechanism and has an inner supportingsurface having an uphole portion and a downhole portion having an inwardtaper complementary to and abutting the shallow taper of the sidesurface of the rupture disc; (ii) an inner sled disposed within theouter sled and which may be operable to move in a downhole directionfrom a first position to a second position or remain stationary in thefirst position after activation of the actuating mechanism and has acylindrical inner surface, a support shoulder in abutment with at leasta segment of the bottom surface of the rupture disc and a bottomsurface; and (iii) a securing mechanism operable to secure the outersled and inner sled in their first positions and release the outer sledand inner sled after activation of the actuating mechanism.

The rupture disc assembly also includes a housing operable to house therupture disc and actuating mechanism, the housing comprising a) an uppertubular member having an upper end, a lower end and an interior surfacedefining a fluid passageway therethrough and b) a lower tubular memberhaving an upper end coupled to the lower end of the upper tubularmember, a lower end and an interior surface defining a fluid passagewaytherethrough and a stop shoulder positioned on the interior surfaceoperable to stop downhole movement of the inner sled and outer sled. Therupture disc is operable to form a temporary seal within the rupturedisc assembly when the inner sled and outer sled are in their firstpositions and to rupture breaking the seal after the inner sled hasmoved to its second position, or in embodiments where the inner sled isstationary after activation, after the outer sled has moved to itssecond position.

The present disclosure also provides an apparatus for forming a buoyantchamber in a well, the apparatus including:

a) a first length of tubing operable to be positioned in the well andhaving an uphole end and a downhole end operable for connection to asecond length of tubing containing a float device operable for forming alower boundary of a buoyant chamber and

b) the rupture disc assembly of the present disclosure including therupture disc, the actuating mechanism and the housing coupled to theuphole end of the first length of tubing and operable for forming anupper boundary of the buoyant chamber during deployment of the buoyantchamber into the well.

The present disclosure also provides a casing string float assemblyincluding a tubular having a lower seal at a lower position of thetubular to form a lower seal, the rupture disc assembly of the presentdisclosure at an upper position of the tubular to form an upper seal anda buoyant chamber positioned between the lower seal and the upper seal.

The present disclosure also provides a method for installing a casingstring in a wellbore, the method comprising: after the casing stringfloat assembly of the present disclosure has been run into a wellborewith a buoyant fluid maintained in the buoyant chamber, applying ahydraulic pressure through the casing string float assembly to applypressure to the pressure facing surface of the rupture disc that is atleast as great as the disc failure trigger pressure to activate theactuating mechanism thereby releasing the securing mechanism allowingthe inner sled to move from the first position to the second position tobreak the rupture disc thereby releasing the buoyant fluid from thebuoyant chamber, or in embodiments where the inner sled is stationaryafter activation, allowing the outer sled to move from its firstposition to second position to break the rupture disc thereby releasingthe buoyant fluid from the buoyant chamber.

The present disclosure also provides a method of installing a casingstring in a wellbore containing a well fluid having a specific gravity,the wellbore having an upper, substantially vertical portion, a lower,substantially horizontal portion, and a bend portion connecting theupper and lower portions, the method comprising: (a) running a casingstring comprising the casing string float assembly of the presentdisclosure into the wellbore, wherein the buoyant chamber comprises afluid having a specific gravity less than the specific gravity of thewell fluid, and (b) floating at least a portion of the casing stringfloat assembly in the well fluid into the lower, substantiallyhorizontal portion of the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described with reference to the attacheddrawings in which:

FIG. 1 is a cross-sectional view of a float tool with a rupture discassembly installed within a casing string in a wellbore;

FIG. 2 is a is a cross-sectional view of a rupture disc assemblyaccording to an embodiment of the present disclosure;

FIG. 2A is an enlarged view of a portion of the rupture disc assembly ofFIG. 2 ;

FIG. 3 is is a perspective view of an outer sled of the rupture discassembly of FIG. 2 ;

FIG. 4 is a perspective view of an inner sled of the rupture discassembly of FIG. 2 ;

FIG. 5 is a cross-sectional view of the rupture disc assembly of FIG. 2;

FIG. 6 is a perspective view of a top ring of the rupture disc assemblyof FIG. 2 ; and

FIG. 7 is a perspective view of a screw of the rupture disc assembly ofFIG. 2 .

DETAILED DESCRIPTION OF EMBODIMENTS

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed apparatus' and/or methods may beimplemented using any number of techniques, whether currently known orin existence. The disclosure should in no way be limited to theillustrative implementations, drawings, and techniques illustratedbelow, including the exemplary designs and implementations illustratedand described herein, but may be modified within the scope of theappended claims along with their full scope of equivalents.

As used herein, the word “vessel” generally means a body that isconfigured to contain or hold a gas or liquid or a mixture thereof, andincludes without limitation, a container and a tubing, for example, apipe including, such as for example, a pipe casing or drill pipe whichmay be used in an oil/gas wellbore. The word “disc” as used in thepresent disclosure is not limited to a component that is generallycircular in shape while the terms “upper” and “top” refer to the upholedirection that is toward the surface of the oil/gas wellbore and theterms “lower” and “bottom” refer to the downhole direction that istoward the toe of the oil/gas wellbore. The terms “abut(s)”, “abutting”and “abutment” are used herein in a broad lay sense to mean next oradjacent to, having a common boundary or in contact directly.

“Disc Rupture Pressure” refers to a minimum pressure applied to apressure facing surface of a rupture disc sufficient to cause therupture disc to rupture or burst. “Acting Pressure” refers to a totalpressure applied to a pressure facing surface of the rupture disc duringa particular operation (e.g. hydrostatic and dynamic when running casingstring into the wellbore). “Disc Failure Trigger Pressure” refers to aminimum pressure applied to a pressure facing surface of the rupturedisc sufficient to activate/trigger an actuating mechanism.

Float Tool

Referring to FIG. 1 , there is shown a float tool comprising a rupturedisc assembly 10 according to an embodiment of the present disclosureinstalled as part of a casing string 94 in a wellbore 92. The wellbore92 is shown as a relatively deep and narrow hole, including a verticalsegment 130 and a horizontal segment 140, although other deviatedwellbores of varying shapes are possible. The wellbore 92 may contain afluid (for e.g. drilling mud (not shown)) and the well is continuouswith a reservoir containing a producible fluid for example, groundwater, oil, a gas or any mixture thereof. In FIG. 1 , the float tool hasalready been run into the wellbore 92 with a gap between the casingstring 94 and the wellbore 92 resulting in an annulus 110.

In operation, the rupture disc assembly 10 may be in a sealing mode, arelease mode or a disc failure mode. When in the sealing mode, therupture disc assembly 10 forms a temporary seal or isolation barrierwhich isolates a fluid-filled upper section 93 of the casing string 94from a buoyant chamber 120 formed in the casing string 94 between therupture disc assembly 10 and a sealing device, such as a float shoe 96,disposed at a lower end of the casing string 94. In the illustratedexample of FIG. 1 , the rupture disc assembly 10 is installed in thecasing string 94 so that it is positioned in the vertical segment 130 ofthe wellbore 92, proximal to a bend 150 leading to the horizontalsegment 140 of the wellbore 92. This placement is not limiting andvariations in the placement of the rupture disc assembly 10 in thecasing string 94 are possible. Generally, the rupture disc assembly 10should be positioned in the casing string 94 to increase or maximizevertical weight on the casing string 94 via the fluid-filled uppersection 93 while reducing or minimizing weight and friction in thehorizontal segment.

In some embodiments, the buoyant chamber 120 is filled with air whichcan reduce the amount of weight needed in the fluid-filled upper section93 to run the casing string 94 into the wellbore 92. However, thebuoyant chamber 120 may be filled with other fluids having a densityless than the fluid in the fluid-filled upper section 93. For example,in some embodiments, the buoyant chamber 120 is filled with a gas, forexample nitrogen, carbon dioxide or other suitable gas. Light liquidsmay also be possible, for example gas condensate. Generally, the buoyantchamber 120 is filled with fluid that has a lower specific gravity thanwell fluid in the wellbore 92 and generally the choice of which gas orliquid to use is dependent on various factors, such as well conditionsand the amount of buoyancy desired.

The rupture disc assembly 10 includes a rupture disc 30 that forms theupper boundary or upper seal of the buoyant chamber 120. The rupturedisc assembly 10 changes from the sealing mode to the release mode whenthe rupture disc is released from the upper seal position and moves in adownhole direction to the disc failure mode when the rupture disc 30 isruptured thus breaking the upper seal as will be further discussedbelow. The rupture disc 30 includes all shapes and configurations ofrupture-type diaphragms, including but not limited to hemisphericaldome-shaped discs 36 as well as flat or substantially flat discs. Therupture disc 30 may be manufactured and calibrated to hold pressure upto a certain magnitude before it ruptures or bursts (i.e. its burstpressure). Thus, the burst pressure of the rupture disc 30 must begreater than the acting pressure in the casing string 94 when the casingstring 94 is being run into the wellbore in order to avoid undesiredrupturing or breaking of the rupture disc 30 in the disc failure mode.Any distance between the float shoe 96 and the rupture disc 30 may beselected in order to provide a sufficient buoyancy force to run thecasing string 94 into the wellbore 92 and to increase or maximize thevertical weight of the casing string 94 via the fluid-filled uppersection 93 as noted above.

The float shoe 96 may form a lower boundary or lower seal of the buoyantchamber 120. As will be appreciated, an alternative float device, suchas a float collar 98, may be used as a substitute for or addition to thefloat shoe 96. Float shoes, float collars and similar devices are hereinreferred to as “float devices”. In the illustrated example, both thefloat shoe 96 and the float collar 98 are included in the casing string94. In some embodiments, the float collar 98 is positioned uphole of thefloat shoe 96. When present, the float collar 98 serves as a redundantfluid inflow prevention means. The float collar 98 is similar inconstruction to the float shoe 96 and includes a valve (not shown) thatprevents wellbore fluid from entering the buoyant chamber 120.Similarly, the float shoe 96 generally includes a check valve (notshown) that prevents inflow of wellbore fluid during the running in orlowering of the casing string 94 into the wellbore 92.

Float shoes 96 are generally known in the art. For example, U.S. Pat.Nos. 2,117,318 and 2,008,818 describe float shoes, the contents of whichare incorporated herein by reference. Float shoes 96 may be closed byassistance with a spring. Once closed, pressure outside the float shoe96 may keep it closed. In some float shoes 96, its check valve can beopened when fluid flow through the casing string 94 is desired, forexample, when cementing operations are to begin. In some cases, thefloat shoe 96 may be drilled out after run-in is complete. When present,the float collar 98 often has a landing surface for a wiper displacementplug. In addition to a float shoe 96 and/or float collar 98, a bafflecollar and/or guide shoe may also be present. The float tool comprisingthe rupture disc assembly 10 shown in the FIG. 1 can be adapted to becompatible with most float shoes, landing collars and float collars.

In some embodiments, the landing collar 100 is positioned between thefloat shoe 96 and the rupture disc assembly 10. The landing collar 100can be present on a surface of the float collar 98 when present. Thelanding collar 100 may be generally used in cementing operations forreceiving cementing plugs, such as a wiper plug. Suitable landingcollars 100 are known in the art, and the float tool does not requirethat a particular landing collar be used, so long as the landing collarhas surface for receiving a plug and so long as the landing collar canbe suitably installed on the casing string 94.

Rupture Disc Assembly

Referring now to FIGS. 2 and 2A, there is shown a rupture disc assembly10 according to an embodiment of the present disclosure. As discussedabove, the rupture disc assembly 10 may form part of the casing string94 shown in FIG. 1 and includes the rupture disc 30. The rupture disc 30has a pressure facing surface at its uphole end, which in someembodiments is generally dome-shaped (as shown in FIG. 1 ). The rupturedisc assembly 10 further includes a bottom surface 30 c at its lowerend, and a side surface having an upper portion 30 a that may begenerally cylindrically shaped and a lower portion 30 b that may begenerally truncated conically shaped such that it has a shallow taperinward towards the bottom surface 30 c of the rupture disc 30. Therupture disc 30 has an inherent static burst pressure based on the size,shape, type, and material quality of the disc, meaning the disc willrupture or break when supported along or near the outer edge of itsbottom surface and when its pressure facing surface is subjected to adisc rupture pressure.

The rupture disc 30 may be composed of any suitable material that hasrelatively high compressive strength and can shatter preferably intosmall pieces. In some embodiments, the rupture disc 30 is composed ofglass. Although silica-free glasses may be employed, in most embodimentsthe glass is comprised of silica (silicon dioxide) with other substancesadded to make the glass easier to work with and/or alter physicalproperties, such as boron trioxide. In other embodiments, the glass maybe strengthened glass, for example thermally (tempered) or chemicallystrengthened soda lime glass.

In other embodiments, the rupture disc 30 is composed of a ceramic.Ceramics include inorganic, non-metallic solids comprising either metalor non-metal compounds. Traditional clay-based ceramics includeporcelain, brick and earthenware. Advanced ceramics are generally notclay based but typically comprise an oxide, such as alumina (Al₂O₃) orzirconia (ZrO₂) or a non-oxide, such as boron carbide (B₄C) or siliconcarbide (SiC).

In still other embodiments, the rupture disc 30 is composed of aglass-ceramic. Glass-ceramics are formed in the same way as a glass,followed by an additional manufacturing step comprising reheatingcausing partial crystallisation to yield a material withhigh-temperature stability, low thermal expansion, high strength andtoughness. An example of a glass-ceramic is a blend of lithium oxide(Li₂O), alumina (Al₂O3) and silica (SiO₂).

The rupture disc assembly 10 may further include a housing defined byone or more tubulars. In one embodiment, the housing is defined by alower tubular member 40 having an upper end, a lower end and an interiorsurface defining a fluid passageway therethrough and an upper tubularmember 45 having an upper end, a lower end and an interior surfacedefining a fluid passageway therethrough. In operation, the lowertubular member 40 defines a lower fluid passageway through its interiorfrom the lower end of the upper tubular member 45 to the buoyant chamber120 and the upper tubular member 45 defines an upper fluid passagewaythrough its interior from the fluid-filled upper section 93 to the upperend of the lower tubular member 40 as shown in FIG. 1 . It should benoted that when the rupture disc 30 has formed a temporary seal, fluidfrom upper section 93 is prevented from passing through to the buoyantchamber 120 and when the rupture disc 30 has broken, fluid from uppersection 93 is able to pass through the upper and lower fluid passagewaysto the buoyant chamber 120.

The upper tubular member 45 and lower tubular member 40 are coupled toone another. In one embodiment, a portion of the lower end of uppertubular member 45 surrounds a portion of the upper end of lower tubularmember 40. The upper tubular member 45 and the lower tubular member 40may be mechanically joined together, for example using a threadedconnection. Other interconnecting methods known to those persons skilledin the art are also possible. One or more seals between upper tubularmember 45 and the lower tubular member 40 can be provided to create afluid seal. In FIG. 2 , the fluid seal is created by an O-ring seal 50.

Although not shown in the illustrated example, the upper tubular member45 can be threaded at its upper end for coupling to other tubularmembers of the casing string 94, and the lower tubular member 40 can bethreaded at its lower end for coupling to other tubular members of thecasing string 94. It is noted that the tubulars members 40 and 45 may becoupled to other tubular members of the casing string 94 using othervarious coupling methods known to those skilled in the art.

In some embodiments, the upper tubular member 45 and the lower tubularmember 40 can have an inner diameter that is similar to or not less thanthe inner diameter of the other tubular members which make up the casingstring 94. In still other embodiments, the upper tubular member 45,lower tubular member 40 or both may have a portion having an innerdiameter that is larger than or expanded as compared to the innerdiameter of the other tubular members which make up the casing string 94to facilitate installation of the rupture disc 30 (see FIG. 2 ). Forexample, in one embodiment the rupture disc 30 may have a diameter ofabout 4.8 inches. The other tubular members making up the casing string94 may have an inner diameter of about 4.5 inches. Thus, at least one ofthe upper tubular member 45 or lower tubular member 40 will have aportion in which its inner diameter is larger than 4.5 inches (i.e. aradially expanded region) to facilitate placement of the rupture disc 30therein. The above is not limiting and other diameters of the rupturedisc 30 and inner diameters of the other tubular members making up thecasing string and tubular members 40 and 45 are possible.

The rupture disc assembly 10 further includes an actuating mechanism 12operable to be activated, and once activated, is operable to change therupture disc assembly 10 from the sealing mode to the release mode andto the disc failure mode. The actuating mechanism 12 may generallyinclude an outer sled 20, an inner sled 25 and a securing mechanism 33.The actuating mechanism 12 is configured to support the rupture disc 30and hold it in sealing engagement when the rupture disc assembly 10 isin the sealing mode and orients the bottom surface 30 c of the rupturedisc 30 toward the buoyant chamber 120 and the pressure facing surfaceof the rupture disc 30 toward the fluid-filled upper section 93 shown inFIG. 1 . The actuating mechanism 12 and rupture disc 30 are operativelycoupled.

With continued reference to FIGS. 2, 2A and to 3 and 4, the outer sled20 and inner sled 25 are configured and operable to move in a downholedirection (and may move independently from one another) from theirinitial or first position when the rupture disc assembly is in thesealing mode to a second position once the actuating mechanism 12 hasbeen activated. The outer sled 20 has an inner supporting surface 21having an uphole portion 21 a and a downhole portion 21 b having agenerally truncated conically shape such that it has an inward tapercomplementary to the shallow taper of the lower portion 30 b sidesurface of rupture disc 30 so that downhole portion 21 b abuts with atleast a segment of the lower portion 30 b side surface. The outer sled20 also includes a cylindrical inner surface 22 below the innersupporting surface 21 sized and configured to allow the inner sled 25 tobe disposed therein, and an outer surface 23.

The inner sled 25 disposed within the outer sled 20 has an outer surface25 a, a cylindrical inner surface 25 b and a support shoulder 26 thatabuts with at least a segment of the bottom surface 30 c of rupture disc30. The inner supporting surface 21 and cylindrical inner lower surface22 of outer sled 20 and cylindrical inner surface 25 b of inner sled 25define a fluid passageway from the upper tubular member 45 to the lowertubular member 40 when the rupture disc assembly 10 is in the discfailure mode. Sleds 20 and 25 may be made from any suitably strongmaterial which is able to withstand downhole conditions, such as steel(e.g. carbon steel, alloy steel, tool steel or stainless steel).

When performing an operation in the oil/gas field (such as running acasing string with a buoyant chamber into a wellbore) and an actingpressure is applied to the pressure facing surface of a rupture disc, atop surface region of the rupture disc is generally in compression whilea bottom surface region of the rupture disc is generally in tension.

According to the embodiments of this disclosure, when an acting pressureis applied to the pressure facing surface of the rupture disc 30,abutment between outer sled 20 and rupture disc 30 at the downholeportion 21 b of inner supporting surface 21 and the lower portion 30 bside surface produces sufficient radial compression in the bottomsurface region of the rupture disc 30 to significantly counteract oreven cancel out the tension in the bottom surface region, especially onthe bottom surface 30 c. Tapering of the inner supporting surface 21 ofouter sled 20 and side surface of rupture disc 30 results in the rupturedisc 30 being able to withstand higher pressures applied to its pressurefacing surface as it is compressed into the tapered support surface.This effectively increases the burst pressure of the disc, permittingthe disc to remain in the sealing mode at pressures greater than theinherent static burst pressure of the disc.

In order to reduce or possibly substantially eliminate tensile stressesin the rupture disc 30 while pressure is being applied to its pressurefacing surface, the shallow taper of the lower portion 30 b side surface(and corresponding inward taper of the downhole portion 21 b of innersupporting surface 21) may be designed and configured to provide a taperangle (the angle formed by the lower portion 30 b side surface andbottom surface 30 c) of about 10 degrees or in other embodiments betweenabout 3 degrees to about 30 degrees, or between about 3 degrees to about20 degrees, or between about 5 degrees to about 15 degrees, or betweenabout 8 degrees to about 12 degrees.

In some embodiments, the shallow taper of the lower portion 30 b sidesurface of rupture disc 30 has a length that spans more than about 30%of the rupture disc's thickness. This can ensure that a sufficientamount of the rupture disc 30 is in compression to significantlymitigate or cancel tensile stresses in the rupture disc 30, especiallyon the bottom surface 30 c. For example, the length of the shallow taperof lower portion 30 b spans more than about 35% or more than about 40%of the thickness of the rupture disc 30. Such embodiments can enable alarge volume of the rupture disc 30 to be in compression at the time ofbreakage/failure to allow it to shatter into fine debris.

As noted above, inner sled 25 includes a support shoulder 26. Supportshoulder 26, shown in more detail in FIG. 2A, extends radially inwardsfrom the outer surface 25 a to the inner surface 25 b of inner sled 25.The support shoulder 26 comprises a contact surface area that isconfigured and operable to engage the bottom surface 30 c of rupturedisc 30 and provide an upward axial force on the bottom surface 30 c tolimit the amount of radial compression rupture disc 30 is subjected towhen the contact surface area and bottom surface 30 c are engaged.Furthermore, incorporation of the support shoulder 26 into the innersled 25 enables the rupture disc 30 to be lifted off of the outer sled'sdownhole portion 21 b of inner supporting surface 21 therebysubstantially reducing or eliminating the added compression forces fromthe taper acting on the rupture disc 30 when the inner sled 25 movesfrom its first position to second position as will be discussed infurther detail below.

In the illustrated embodiment shown in FIGS. 2 and 2A, the outer sled 20and inner sled 25 are depicted in their first position relative to theupper tubular member 45 and lower tubular member 40 when the rupturedisc assembly 10 is in the sealing mode. The actuating mechanism 12includes a securing mechanism 33 that may be, for example, a shear ring,that is configured and operable to secure the outer sled 20 and innersled 25 to the upper and lower tubular members 45 and 40 in their firstpositions and release the outer sled 20 and inner sled 25 when thepressure facing surface of rupture disc 30 is subjected to the discfailure trigger pressure. In particular, in operation the shear ring 33is operable to prevent downhole movement of the outer and inner sleds 20and 25 relative to the upper and lower tubular members 45 and 40 when anacting pressure (which is below the disc failure trigger pressure anddisc rupture pressure as referenced above) or a range of such actingpressures is applied to the pressure facing surface of the rupture disc30. Thus, during the running in of a casing string 94 into the wellbore92 (shown in FIG. 1 ), the maximum acting pressure applied to thepressure facing surface of the rupture disc 30 can not exceed the discfailure trigger pressure in order to maintain the rupture disc assemblyin the sealing mode. When it's desired to change the rupture discassembly 10 to the disc failure mode, the actuating mechanism 12 may beactivated by increasing the acting pressure to a pressure at or abovethe disc failure trigger pressure. The shear ring 23 is configured tobreak when the pressure facing surface of rupture disc 30 is subjectedto the disc failure trigger pressure thereby activating the actuatingmechanism 12. Upon such activation, rupture disc assembly 10 moves fromthe sealing mode to the release mode (i.e. the outer and inner sleds 20and 25 are released from restraint and begin to move downhole relativeto the lower and upper tubular members 40 and 45 towards their secondpositions). More specifically, subjecting the pressure facing surface ofthe rupture disc 30 to acting pressure that is at or exceeds the discfailure trigger pressure causes the shear ring 33 to break therebyreleasing the inner and outer sleds 20 and 25 from restraint andenabling the movement of the sleds 20 and 25 downhole towards theirsecond positions and thus changing the rupture disc assembly 10 to therelease mode. The disc failure trigger pressure can be, for example,between about 2,500 psi to about 8,500 psi, depending on the materialsand configuration of the shear ring 33. In some embodiments, the discfailure trigger pressure may even be greater, for example between about10,000 psi to about 14,000 psi, or even greater than about 14,000 psi. Aload ring 34 may be used to ensure that an even pressure is applied toshear ring 33 from outer and inner sleds 20, 25 and prevent undesired orpremature breaking of shear ring 33 before the disc failure triggerpressure is reached.

While shear ring 33 is an example of a securing mechanism forrestraining movement, other securing mechanisms may be used, such asshear pins, shear tabs or other shearable devices like a collet.

With reference to FIGS. 2, 5, 6, and 7 , the rupture disc assembly 10may further include a ring 330. Ring 330 is sized and configured to abutthe uphole portion 21 a of inner supporting surface 21 of outer sled 20to assist in securing the rupture disc 30. The ring 330 may be securedto the outer sled 20, such as by a threaded connection, and is operableto move in a downhole direction with the outer sled 20 upon activationof the actuating mechanism. Ring 330 does not need to be a seal and canbe retained in the housing even after the rupture disc 30 breaks toavoid its release to the wellbore, Ring 330, shown in greater detail inFIG. 6 , may have an inner diameter less than the inner diameter of theupper portion 30 a side surface and an impact surface on its bottom endwhich may include a plurality of inwardly projecting spaced apart ridges332 or in some embodiments, a plurality of screws which may be comprisedof nylon or plastic or a plurality of tips which may be comprised ofcarbide. Ring 330 may also include a number of holes 334 for receivingscrews 340 therethrough. As shown in FIG. 5 , when installed, screws 340protrude from the bottom end of ring 330. Through this configuration,rupture disc 30 is maintained in the position shown in FIG. 5 and avoidsdirect contact with the bottom end impact surface of ring 330. This mayprevent any undesired impacts between rupture disc 30 and ring 330 thatmay cause unintentional breakage of the rupture disc 30, for exampleduring shipping and installation of rupture disc assembly 10. An exampleof a suitable screw 340 is shown in FIG. 7 , and in some embodiments maybe comprised of plastic or nylon.

As noted above, upon activation of the actuating mechanism 12, thesecuring mechanism 33 (i.e. shear ring) releases the outer and innersleds 20, 25 from their securement with the lower and upper tubularmembers 40 and 45 allowing the inner sled 25 and outer sled 20 to beginmovement in the downhole direction towards stop shoulder 40 a of lowertubular member 40. Stop shoulder 40 a is operable to prevent furtherdownhole movement of the sleds 20 and 25 upon contact with the lowerends of sleds 20 and 25 (i.e. the inner and outer sleds have moved totheir second positions when their lower ends contact stop shoulder 40a). Because the lower end of inner sled 25 is positioned furtherdownhole than the lower end of outer sled 20 when they are in theirfirst positions, the lower end of inner sled 25 will contact stopshoulder 40 a before the lower end of outer sled 20 and inner sled's 25downhole movement will therefore stop before the outer sled's 20downhole movement stops. Accordingly, inner sled 25 will reach itssecond position before the outer sled 20 reaches its second position.

Thus, during operation and after activation of the actuating mechanism,inner and outer sleds 25 and 20, along with rupture disc 30 and ring330, will begin to move in a downhole direction in the release mode.When inner sled 25 reaches its second position, its downhole movementwill stop while the outer sled 20, rupture disc 30 and ring's 330movement in the downhole direction will continue. This decoupling ofmovement of the inner sled 25 and the outer sled 20 effectively allowsthe upward axial force produced by the contact surface area of supportshoulder 26 on the bottom surface 30 c of rupture disc 30 to temporarilylift the rupture disc 30 off of the downhole portion 21 b of innersupporting surface 21 of the outer sled 20. This temporary lift ordisengagement of rupture disc 30 from outer sled 20 reduces oreliminates the taper-induced radial compression in the lower region ofrupture disc 30 which in turn reduces the disc rupture pressure at whichthe rupture disc 30 will shatter/break in the disc failure mode. If thereduced disc rupture pressure is less than the acting pressure at thattime, the rupture disc 30 will shatter/break while if it is greater thanthe acting pressure at that time the rupture disc 30 will notshatter/break. In this case, continued downhole movement of the outersled 20 and ring 330 will result in the impact surface on the bottom endof ring 330 to contact/collide with the rupture disc 30 imparting animpact force to the rupture disc 30 that is sufficient to shatter/breakrupture disc 30. When the impact surface comprises ridges 332 (or screwsor tips), the impact force is imparted to the rupture disc 30 in aplurality of point loads which may further assist in ensuring thatrupture disc 30 will shatter/break. Furthermore, if the rupture disc 30is still temporarily disengaged from the inner supporting surface 21 ofthe outer sled 20 when the impact surface of the ring 330 collides withthe rupture disc 30, the impact force required to shatter/break therupture disc 30 will be lower than if the rupture disc 30 was stillengaged with the inner supporting surface 21. Thus, in such embodiments,breaking of the rupture disc 30 can occur from a force produced by:application of acting pressure on the rupture disc; application of animpact force on the rupture disc produced by downhole movement andcontact by ring 330; or, by application of such forces in combination.

As noted above, in some embodiments, the inner sled 25 remainsstationary in its first position when the rupture disc assembly 10 is inthe release and disc failure mode. In these embodiments, upon activationof the actuating mechanism 12, the securing mechanism 33 (i.e. shearring) releases the outer sled 20 and inner sled 25, from securement withthe lower and upper tubular members 40 and 45 allowing the outer sled 20to begin movement in the downhole direction towards stop shoulder 40 aof lower tubular member 40. The inner sled 25 is configured so that itslower end is already engaged with stop shoulder 40 a or other ledge whenthe rupture disc assembly 10 is in the sealing mode and will not move inthe downhole direction after the actuating mechanism 12 is activated.Again, stop shoulder 40 a is operable to prevent downhole movement ofouter sled 20 upon contact with the lower end of outer sled 20 (i.e. thelower end of the inner sled 25 is in contact with stop shoulder 40 a orother ledge and is stationary and therefore remains in the firstposition and outer sled 20 moves from the first position to the secondposition when its lower end contacts stop shoulder 40 a). The lower endof inner sled 25 is positioned further downhole than the lower end ofouter sled 20 when they are in their first positions and therefore theouter sled 20 will be movably disposed over inner sled 25 after theactuating mechanism 12 is activated.

During operation and after activation of the actuating mechanism, outersled 20, but not inner sled 25, along with rupture disc 30 and ring 330,will begin to move in a downhole direction in the release mode towardsstop shoulder 40 a. When the lower end of outer sled 20 reaches stopshoulder 40 a, such movement will stop. During downhole movement, theimpact surface on the bottom end of ring 330 will contact/collide withthe rupture disc 30 imparting an impact force to the rupture disc 30that is sufficient to shatter/break rupture disc 30 in the disc failuremode. When the impact surface comprises ridges 332 (or screws or tips),the impact force is imparted to the rupture disc 30 in a plurality ofpoint loads which may further assist in ensuring that rupture disc 30will shatter/break. As described above, if the rupture disc 30 istemporarily disengaged from the inner supporting surface 21 of the outersled 20 when the impact surface of the ring 330 collides with therupture disc 30, the impact force required to shatter/break the rupturedisc 30 will be lower than if the rupture disc 30 was still engaged withthe inner supporting surface 21. Thus, in such embodiments, breaking ofthe rupture disc 30 can occur from a force produced by: application ofacting pressure on the rupture disc; application of an impact force onthe rupture disc produced by downhole movement and contact by ring 330;or, by application of such forces in combination

In some embodiments, the outer sled 20 may include a void 32 (see FIG. 3) surrounding its outside surface 23 to reduce or eliminate frictionbetween the outer sled 20 and inner surface of upper tubular member 45in order to enhance downhole movement of the outer sled 20 after theactuating mechanism 12 has been activated. The void 32 may also permitthe outer sled 20 to undergo some level of flexing/deformation/strainwhen the rupture disc 30 is subjected to an acting pressure which mayassist in allowing compression to develop in the disc 30, particularlyin a region of the disc 30 where the tapered surface is located. Inaddition, the void 32 can provide a fluid path through which externalpressure via fluid above the rupture disc assembly 10 can be applied toan upper portion of the outer sled 20 which can further increase theradial compression on the rupture disc 30.

Referring to FIGS. 2 and 2A, the disc activation mechanism 12 mayfurther include a lock ring 27. Lock ring 27 is configured and operableto engage with a corresponding groove 28 in the outer sled 20 once theouter sled 20 reaches its second position thereby locking the outer sled20 in the second position. However, other known locking mechanismsbesides a lock ring are possible.

In still other embodiments, the rupture disc assembly 10 may includeannular seals 38 and 39 (e.g. an O-ring seal) positioned around theupper portion 30 a of the side surface of the rupture disc 30 and outersurface of outer sled 20 (See FIGS. 2 and 2A). The annular seals 38, 39can assist in preventing leakage between the outer sled 20 and therupture disc 30 and upper tubular member 45 and/or prevent friction andpremature breakage of the rupture disc 30. In some embodiments, to avoidrelease of the annular seals 38 and 39 into the wellbore when therupture disc 30 breaks, the annular seals may be created by moulding abonded rubber seal to the outer sled 20. In some embodiments, a preloadapplied to the rupture disc 30, upper tubular member 45 and the outersled 20 during installation can create a seal between the rupture disc30, upper tubular member 45 and the outer sled 20 thereby avoiding anyneed for the annular seals.

In the illustrated embodiment, the rupture disc 30 is shown to have aspecific geometry. As indicated above, the specific geometry includes aside surface having a truncated cone shape for a bottom portion 30 b anda cylindrical shape for a top portion 30 a. Notably, there is no taperwith the cylindrical shape, but the truncated conical shape provides theshallow angle taper described above. However, it is to be understoodthat other geometries are possible for rupture disc 30. In general,geometries that enable radial compression on the bottom surface 30 c canbe employed. Note that this can include shapes in which voids orcut-outs are present. While the illustrated embodiment shows the bottomsurface 30 c of the rupture disc 30 as generally flat, other shapes mayfurther improve the radial compression on the bottom surface 30 or lowerregion of the disc 30. For example, the bottom surface 30 c may beconcave-shaped. The concave-shaped surface is an example in which a voidor cut-out is present which may further increase radial compressivestress in the rupture disc 30, particularly in its lower region. Thecompressive stress in the rupture disc 30 is increased by volumereduction compared to a rupture disc 30 without a concave-shaped bottomsurface. The rupture disc 30 with the concave-shaped bottom surface mayalso reduce the amount of debris released to the wellbore 92, which maybecome important for larger sized airlocks with large disc thicknessesand diameters.

In some embodiments friction between the side surface of the rupturedisc 30 and the inner supporting surface 21 of the outer sled 20 mayoccur and such friction can depend on various factors, such as the taperangle. Thus, a lubricant may be disposed between the upper and/or lowerportions 30 a and 30 b (particularly the lower portion 30 b) of the sidesurface of rupture disc 30 and/or the uphole and downhole portions 21 aand 21 b of inner supporting surface 21 of the outer sled 20 tofacilitate a sliding engagement between the rupture disc 30 and theouter sled 20 that assists in allowing the rupture disc 30 to be wedgedinto and supported by the supporting surface 21 and radial compressiveforces to be applied to the rupture disc 30. With such lubrication, thefriction between rupture disc 30 and the outer sled 20 can be reduced,and some amount of movement of the rupture disc 30 into the outer sled20 is permitted while pressure is applied to the pressure facing surfaceof the rupture disc 30. In other embodiments a lubricant may be disposedbetween the outer surface 25 a of inner sled 25 and the inner surface 22of outer sled 20. In some embodiments, the lubricant includes a grease.However, other lubricants or other materials to permit such movement maybe employed, for example, Teflon-based compounds or API pipe lubricant(Copper-Kote).

According to the embodiments described above, the rupture disc assembly10 functions as a temporary upper seal for the buoyant chamber 120 inthe casing string 94 shown in FIG. 1 . However, it is to be understoodthat this is one application and that other applications are possibleand within the scope of this disclosure. In some embodiments, therupture disc assembly 10 is used to create a temporary seal for anysuitable tubing. The tubing can be a casing string as described above, aliner, or any other suitable tubing. However, other applications thatmay not involve tubing are possible. More generally, the rupture discassembly 10 can be used in a tank, a pressure vessel, a frac port, orany other suitable vessel. For example, the temporary seal created bythe rupture disc assembly 10 may be useful as a safety measure, forexample, to limit how much pressure is permitted inside the tank orpressure vessel and enabling the rupture disc 30 to break beforepressure inside the tank reaches a dangerous level. In the case of afrac port, for example, the rupture disc assembly 10 can be used forcreating a temporary seal for the frac port.

Method of Installing Casing String

Referring to FIG. 1 , the rupture disc assembly 10, can be used in amethod for installing a casing string in a wellbore, and in a method tofloat a casing during the installation of the casing string 94 in thewellbore 92. As noted above, running a casing string in a deviatedwellbore, especially with long horizontal segments, can result insignificant drag forces. The casing string 94 may become stuck beforereaching a desired location. This is especially the case when downholeforces produced by pushing the weight of the casing string 94 in thewellbore 92 are less than the uphole drag forces. When higher forces areapplied to try and push the casing string 94 further into the wellbore92, damage to the casing string 94 can result.

In a method of installing a casing string 94, the casing string 94 isinitially made up at the surface. There may be one or more pup joints orsimilar piping installed. The landing collar is then installed on thecasing string 94. In some embodiments, drilling mud is added to ensurethat the float shoe 96 is functioning properly. Generally, no fluid isadded to the casing string 94 prior to installing the rupture discassembly 10 (unless a liquid or a gas other than air is to be used tofill the buoyant chamber 120). Once a desired amount of the casingstring 94 has been run into the wellbore 92, the rupture disc assembly10 is installed, trapping air within the casing between the float shoe96 and the rupture disc assembly 10. A remaining amount of the casingstring 94 is then run into the wellbore 92 until the friction dragbetween the casing string 94 with the walls of the wellbore 92 will notallow the casing string 94 to be run to a greater depth. When run to adesired or maximum depth, the float shoe 96 may be located at the heelof the well, or within the horizontal segment of the well some distancefrom the “toe” or bottom of the wellbore 92. The rupture disc assembly10 may be positioned in the vertical segment 130 of the wellbore 92 ornear the heel. The weight of the casing string 94 in the verticalsegment 130 assists in overcoming the friction drag to allow the casingstring 94 to be positioned at a greater depth, and/or to be movedhorizontally in the wellbore 92. An acting pressure during run-in mustbe less than the burst pressure of the rupture disc 30, to preventpremature rupture of the rupture disc 30 (and must also remain below thedisc failure trigger pressure). Generally, the rupture disc assembly 10may have a pressure rating of 7,500 to 30,000 psi, for example.

Once the casing string 94 has been run and landed, circulating equipmentmay be installed. The rupture disc 30 may then be burst by pressuringthe casing string 94 from the surface to the disc failure triggerpressure. To accomplish this, acting pressure (e.g., from the surface)is applied through the casing string 94. The acting pressure exertsforce on the pressure facing surface of the rupture disc 30, and on theactuating mechanism 12 supporting the rupture disc 30 in place, asdiscussed above. When the acting pressure reaches or exceeds the discfailure trigger pressure, the actuating mechanism 12 is activatedtriggering the movable sleds 20, 25, rupture disc 30 and ring 330 tomove downhole causing the subsequent shattering/breaking of the rupturedisc 30 to change the rupture disc assembly 12 to the disc failure mode,as previously described. Once the rupture disc 30 has burst, fluidpumping may be continued for a short time, and then stopped. Rupture ofthe rupture disc 30 should be evident from the surface by observation ofa pressure drop in the casing string 94.

After the steps involved in installing the float tool into the wellbore92 have been performed to place the rupture disc assembly 10 in thesealing mode, and the rupture disc 30 has been ruptured thereby changingthe rupture disc assembly to the disc failure mode, additionaloperations can be performed. Fluid flow through the casing string 94 canallow air or other fluid or gas that was in the buoyant chamber 120 torise to the surface and be vented from the casing string 94, forexample. The casing string 94 can then be filled with other fluid (fore.g. non-flotation fluid). For example, the casing string 94 can befilled with drilling fluid. When the float shoe 96 is opened,conventional cementing operations can begin. It is also possible to usethe float tool of the present disclosure in reverse cementingoperations. In reverse cementing, a cement slurry can be pumped down theannulus 110 rather than through the casing string 94. When cementingoperations are performed, a cement plug is delivered through the casingstring 94.

In a preferred embodiment, once the rupture disc 30 has been ruptured,an inside diameter of the casing string 94 in a region where the rupturedisc assembly 10 is installed is substantially the same as, or not lessthan, or greater than an inside diameter of the tubular members makingup the remainder of the casing string 94. In an embodiment, the rupturedisc 30 may be installed in a widened region of the casing string 94(for e.g. within radially expanded portions of one or more of the upperor lower tubulars members, the tubular members being connectable toother tubulars in the casing string 94). The ability to restore theinside diameter of the casing string 94 where the rupture disc assemblyis placed is especially useful since downhole tools and the like can bedeployed into the casing string 94 without restriction once the rupturedisc 30 has been broken, and without the need to remove any part of thefloat tool. Because the inside diameter if the casing string 94 isrestored, the present method and the float tool are especially useful inball drop, plug, shifting tool systems etc.

Numerous modifications and variations of the present disclosure arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practised otherwise than as specifically described herein.

1. A rupture disc assembly for use in a vessel, the rupture discassembly comprising: a rupture disc comprising a pressure facingsurface, a bottom surface, and a side surface having a shallow taperinward towards the bottom surface of the rupture disc; an actuatingmechanism configured to support the rupture disc and operable to beactivated when the pressure facing surface of the rupture disc issubjected to a disc failure trigger pressure, the actuating mechanismcomprising: i) an outer sled operable to move in a downhole directionfrom a first position to a second position after activation of theactuating mechanism, the outer sled comprising an inner supportingsurface having an uphole portion and a downhole portion having an inwardtaper complementary to and abutting the shallow taper of the sidesurface of the rupture disc and a bottom surface; ii) an inner sleddisposed within the outer sled and operable to move in a downholedirection from a first position to a second position after activation ofthe actuating mechanism, the inner sled comprising a cylindrical innersurface, a support shoulder configured to abut with at least a segmentof the bottom surface of the rupture disc and a bottom surface downholefrom the bottom surface of the outer sled; iii) a securing mechanismoperable to secure the outer sled and inner sled in their firstpositions and release the outer sled and inner sled after activation ofthe actuating mechanism; wherein the rupture disc is operable to form atemporary seal within the rupture disc assembly when the outer sled andinner sled are in their first positions and, after activation of theactuating mechanism, to break after the inner sled reaches its secondposition.
 2. The rupture disc assembly of claim 1, further comprising ahousing configured to house the rupture disc and actuating mechanism,the housing comprising a) an upper tubular member having an upper end, alower end and an interior surface defining a fluid passagewaytherethrough and b) a lower tubular member having an upper end coupledto the lower end of the upper tubular member, a lower end and aninterior surface defining a fluid passageway therethrough with a stopshoulder positioned on the interior surface operable to stop downholemovement of the inner sled at its second position when the bottomsurface of the inner sled contacts the stop shoulder.
 3. The rupturedisc assembly of claim 2 wherein the actuating mechanism furthercomprises a ring abutting an uphole portion of the inner supportingsurface of the outer sled and having an impact surface and wherein thering is operable to move in downhole direction after activation of theactuating mechanism.
 4. The rupture disc assembly of claim 3, whereinthe impact surface comprises a plurality of spaced apart ridges on abottom surface of the hollow ring.
 5. The rupture disc assembly of claim4, wherein in operation, in response to the pressure facing surface ofthe rupture being subjected to pressure at least equal to the disctrigger pressure, the actuating mechanism is activated and the securingmechanism releases the outer sled and inner sled allowing the outer sledand inner sled to begin to move in a downhole direction wherein movementof the inner sled stops at its second position while movement of theouter sled and ring continues and wherein the rupture disc breaks inresponse to the pressure facing surface being subjected to: a discrupture pressure; the impact surface of the ring; or a combinationthereof.
 6. The rupture disc assembly of claim 1, wherein the securingmechanism comprises a shear ring.
 7. The rupture disc assembly of claim1, wherein the actuating mechanism further comprises a lock ringoperable to lock the outer sled in its second position.
 8. An apparatusfor forming a buoyant chamber in a well, the apparatus comprising: a) afirst length of tubing operable to be positioned in the well and havingan uphole end and a downhole end operable for connection to a secondlength of tubing having a float device operable for forming a lowerboundary of a buoyant chamber and b) the rupture disc assembly of claim2 coupled to the uphole end of the first length of tubing and operablefor forming an upper boundary of the buoyant chamber during deploymentof the buoyant chamber into the well.
 9. A casing string float assemblycomprising a tubular having a lower seal in a lower position of thetubular, the rupture disc assembly of claim 1 at an upper position ofthe tubular to form an upper boundary and a buoyant chamber positionedbetween the lower boundary and the upper boundary.
 10. A method forinstalling a casing string in a wellbore, the method comprising: after acasing string float assembly of claim 7 has been run into a wellborewith a buoyant fluid maintained in the buoyant chamber, applyinghydraulic pressure through the casing string float assembly to apply apressure to the pressure facing surface of the rupture disc that is atleast as great as the disc trigger pressure to cause the actuatingmechanism to activate thereby releasing the securing mechanism to causethe inner sled to move from the first position to the second positionand break the rupture disc thereby releasing the buoyant fluid from thebuoyant chamber.
 11. A method of installing a casing string in awellbore containing a well fluid having a specific gravity, the wellborehaving an upper, substantially vertical portion, a lower, substantiallyhorizontal portion, and a bend portion connecting the upper and lowerportions, the method comprising: (a) running a casing string comprisingthe casing string float assembly of claim 7 into the wellbore, whereinthe buoyant chamber comprises a fluid having a specific gravity lessthan the specific gravity of the well fluid, and (b) floating at least aportion of the casing string float assembly of 7 in the well fluid intothe lower, substantially horizontal portion of the wellbore.
 12. Arupture disc assembly for use in a vessel, the rupture disc assemblycomprising: a rupture disc comprising a pressure facing surface, abottom surface, and a side surface having a shallow taper inward towardsthe bottom surface of the rupture disc; an actuating mechanismconfigured to support the rupture disc and operable to be activated whenthe pressure facing surface of the rupture disc is subjected to a discfailure trigger pressure, the actuating mechanism comprising: an outersled operable to move in a downhole direction from a first position to asecond position after activation of the actuating mechanism, the outersled comprising an inner supporting surface having an uphole portion anda downhole portion having an inward taper complementary to and abuttingthe shallow taper of the side surface of the rupture disc and a bottomsurface; an inner sled disposed within the outer sled and operable toremain stationary in a first position after activation of the actuatingmechanism, the inner sled comprising a cylindrical inner surface, asupport shoulder configured to abut with at least a segment of thebottom surface of the rupture disc and a bottom surface downhole fromthe bottom surface of the outer sled; a securing mechanism operable tosecure the outer sled and inner sled in their first positions andrelease the outer sled and inner sled after activation of the actuatingmechanism; wherein the rupture disc is operable to form a temporary sealwithin the rupture disc assembly when the outer sled and inner sled arein their first positions and, after activation of the actuatingmechanism, to break after the outer sled reaches its second position.13. The rupture disc assembly of claim 12, further comprising a housingconfigured to house the rupture disc and actuating mechanism, thehousing comprising a) an upper tubular member having an upper end, alower end and an interior surface defining a fluid passagewaytherethrough and b) a lower tubular member having an upper end coupledto the lower end of the upper tubular member, a lower end and aninterior surface defining a fluid passageway therethrough and a stopshoulder positioned on the interior surface operable to stop downholemovement of the outer sled at its second position when the bottomsurface of the inner sled contacts the stop shoulder.
 14. The rupturedisc assembly of claim 13 wherein the actuating mechanism furthercomprises a ring abutting an uphole portion of the inner supportingsurface of the outer sled and having an impact surface and wherein thering is operable to move in downhole direction after activation of theactuating mechanism.
 15. The rupture disc assembly of claim 14, whereinthe impact surface comprises a plurality of spaced apart ridges on abottom surface of the ring.
 16. The rupture disc assembly of claim 15,wherein in operation, in response to the pressure facing surface of therupture being subjected to hydraulic pressure at least equal to the disctrigger pressure, the actuating mechanism is activated and the securingmechanism releases the outer sled and inner sled wherein the inner sledremains stationary and the outer sled moves in a downhole directionuntil it reaches its second position and the rupture disc breaks inresponse to the pressure facing surface being subjected to: a pressureof at least a disc rupture pressure; the impact surface of the ring; ora combination thereof.
 17. The rupture disc assembly of claim 12,wherein the securing mechanism comprises a shear ring.
 18. The rupturedisc assembly of claim 12, wherein the actuating mechanism furthercomprises a lock ring operable to lock the outer sled in its secondposition.
 19. An apparatus for forming a buoyant chamber in a well, theapparatus comprising: a) a first length of tubing operable to bepositioned in the well and having an uphole end and a downhole endoperable for connection to a second length of tubing having a floatdevice operable for forming a lower boundary of a buoyant chamber and b)the rupture disc assembly of claim 13 coupled to the uphole end of thefirst length of tubing and operable for forming an upper boundary of thebuoyant chamber during deployment of the buoyant chamber into the well.20. A casing string float assembly comprising a tubular having a lowerseal in a lower position of the tubular, the rupture disc assembly ofclaim 12 at an upper position of the tubular to form an upper boundaryand a buoyant chamber positioned between the lower boundary and theupper boundary.
 21. A method for installing a casing string in awellbore, the method comprising: after a casing string float assembly ofclaim 20 has been run into a wellbore with a buoyant fluid maintained inthe buoyant chamber, applying hydraulic pressure through the casingstring float assembly to apply a pressure to the pressure facing surfaceof the rupture disc that is at least as great as the disc triggerpressure to cause the actuating mechanism to activate thereby releasingthe securing mechanism to cause the outer sled to move from the firstposition to the second position and break the rupture disc therebyreleasing the buoyant fluid from the buoyant chamber.
 22. A method ofinstalling a casing string in a wellbore containing a well fluid havinga specific gravity, the wellbore having an upper, substantially verticalportion, a lower, substantially horizontal portion, and a bend portionconnecting the upper and lower portions, the method comprising: (a)running a casing string comprising the casing string float assembly ofclaim 20 into the wellbore, wherein the buoyant chamber comprises afluid having a specific gravity less than the specific gravity of thewell fluid, and (b) floating at least a portion of the casing stringfloat assembly of 20 in the well fluid into the lower, substantiallyhorizontal portion of the wellbore.